Shock-release fluid fracturing method and apparatus

Abstract

A shock tool is adapted to a bottom hole tool assembly for isolating a zone in a subterranean formation accessed by a wellbore. Fracturing fluid such as nitrogen is accumulated at fracturing pressures uphole of the shock tool for subsequent and rapid release to the formation. The tool assembly can be suspended from a conveyance string in which fluid is accumulated for shock release through a valve of the shock tool and through an injection tool to the zone isolated by the injection tool. After a first zone is shocked, the tool assembly can be moved to a new zone, or multiple shocks can be applied cyclically at the selected zone.

1. A method for fracturing subterranean formations penetrated by a wellbore comprising:
 accessing the formation with a conveyance string having a bore and extending downhole through the wellbore for conveying a tool to the formation; 
 isolating a zone with the tool, the tool having an uphole seal and a downhole seal spaced uphole and downhole of the isolated zone; 
 closing the bore of the conveyance string at a valve at the tool, the valve having a main piston which is biased to close the valve and is pressure-actuated to open the valve, the closing of the bore accumulating a gaseous fracturing fluid along an entirety of the conveyance string or wellbore uphole of the valve, the gaseous fracturing fluid being accumulated to a threshold pressure; 
 opening the bore of the conveyance string at the valve at the threshold pressure, the opening of the bore further comprising
 pressure-actuating a poppet piston at the threshold pressure for triggering unlocking of the main piston, 
 pressure-actuating the unlocked main piston to overcome the main piston biasing for opening the valve so as to communicate with the isolated zone for releasing the accumulated gaseous fracturing fluid, from along substantially the entirety of the conveyance string or the wellbore uphole of the valve, to the isolated zone to shock fracture the formation; and 
 
 closing the valve comprising
 biasing the main piston closed at the resetting pressure; and 
 resetting the poppet piston with the main piston closed for locking the main piston closed. 
 
 
     
     
       2. The method of  claim 1  further comprising, after releasing the fracturing fluid:
 closing the fracturing fluid from communication with the isolated zone; 
 re-accumulating fracturing fluid; and 
 releasing the fracturing fluid to the isolated zone so as to shock fracture the formation. 
 
     
     
       3. The method of  claim 1  further comprising:
 isolating a new zone in the subterranean formation; 
 accumulating fracturing fluid to the threshold pressure; and 
 releasing the fracturing fluid to the new isolated zone and shock fracture the formation. 
 
     
     
       4. The method of  claim 1  wherein:
 the opening of the bore of the conveyance string at the valve further comprises releasing the accumulated gaseous fracturing fluid through a port in the tool to communicate with the isolated zone and shock fracture the formation. 
 
     
     
       5. A tool assembly for shock fracturing a subterranean formation penetrated by a wellbore, the tool assembly conveyed on a conveyance string positioned downhole in the wellbore at a position adjacent the formation and forming an annulus therebetween which is in fluid communication with the formation, the tool assembly comprising:
 an injection tool having an uphole seal and a downhole seal adapted for isolating the annulus uphole and downhole of a zone in the formation, an injection bore at an inlet end uphole of the uphole seal, and an injection port communicating between the bore and the isolated zone; and 
 a shock tool having an inlet and a bore in communication with the injection bore, the shock tool bore having a valve with a pressure-actuated poppet piston biased for locking the valve in a closed position and pressure-actuated for unlocking the valve fit to the inlet, 
 wherein 
 gaseous fracturing fluid is accumulated along an entirety of the conveyance string or the wellbore uphole of the inlet at a fluid pressure when the valve is locked in its closed position, and 
 when the fluid pressure reaches a threshold pressure, the poppet piston is pressure-actuated for unlocking the valve for triggering pressure-actuated opening of the valve for releasing the accumulated fracturing fluid from substantially the entirety of the conveyance string or the wellbore uphole of the inlet through the shock tool to the injection port for shock fracturing the formation, and 
 when the fluid pressure reaches a resetting pressure below the threshold pressure, the valve is biased to close and the poppet piston is biased to lock the valve in its closed position. 
 
     
     
       6. The tool assembly of  claim 5  wherein:
 the inlet of the shock tool is in communication with the wellbore uphole of the uphole seal; and 
 fracturing fluid is accumulated in the wellbore. 
 
     
     
       7. The tool assembly of  claim 5  wherein:
 the shock tool is suspended from the conveyance string extending downhole through the wellbore; 
 the conveyance string having a bore in communication with the bore of the shock tool at the inlet; and 
 the fracturing fluid is accumulated in the bore of the conveyance string uphole of the inlet of the shock tool. 
 
     
     
       8. The tool assembly of  claim 5  wherein the valve further comprises a main piston movable axially in a piston bore having a discharge port being formed along the piston bore, the main piston being biased for blocking the discharge port by the main piston for closing the valve and pressure-actuable for shifting the main piston to unblock the discharge port for opening the valve. 
     
     
       9. The tool assembly of  claim 8  further comprising a sleeve fit to a tubular body for forming a bypass annulus therebetween, the main piston being axially movable in the sleeve for opening and closing the discharge port being formed through the sleeve, the bypass annulus being in communication with the injection port. 
     
     
       10. The tool assembly of  claim 9  further wherein:
 the poppet piston is movable axially in a poppet bore formed in the main piston, the poppet piston further comprising a trigger spool having one or more axially spaced annular release recesses; 
 the sleeve has one or more axially spaced locking recesses formed therein; and 
 the main piston has one or more locking ports extending between the poppet bore adjacent the trigger spool and the sleeve, the poppet further comprising one or more locking elements movable in the locking ports, alternately,
 when the locking ports are misaligned from the trigger spool's release recesses, the locking elements straddle between the main piston and the sleeve's annular locking recesses, wherein the main piston is locked and closed, and 
 when the locking elements align with the trigger spool's release recesses, the locking elements straddle between the locking ports and the trigger spool's release recesses, wherein the main piston is unlocked and released to open. 
 
 
     
     
       11. The tool assembly of  claim 10  wherein the poppet piston is pressure-actuable at the threshold pressure to align the trigger piston's release recesses with the locking ports to unlock the main piston. 
     
     
       12. The tool assembly of  claim 10  wherein when the main piston is unlocked, the main piston is pressure-actuated to open the discharge port. 
     
     
       13. The tool assembly of  claim 10  wherein when the main piston is biased to close at the resetting pressure, the main piston moves axially to align the locking ports with the sleeve's locking recesses to reset the trigger spool and poppet piston and lock the main piston.